Wednesday, 28 September 2016
Sunday, 18 September 2016
A lot of structures have a regularity to them that is useful to emulate, whether it be fences, walls, windows, rows of houses, tree, or chimney pots. As with the fence-post problem you can't implement them as a straight repeat of a single object though since you need one more post than fence panels.
|The Fence-post Problem: N panels but N+1 posts.|
Before we look at solving this however, we will start simpler; looking at how we can handle instancing of the more-straightforward repeating structures.
|Example of a simple array of objects.|
Apparance doesn't yet support arrays as a data-type, arraying of objects, or any form of looping, but an effective alternative that is supported well is recursion. Here we can break down a repeating problem into successive; sub-division, geometry instantiation, and recursion, until the space is filled.
|Basic recursion used for repeating geometry.|
The process of split+generate is invoked on the left split area each time until there is no more to split.
The process of sub-division can be improved somewhat in a couple of ways; first, instead of creating a chain of recursions, one-deeper-per-instance, we can tackle it with successive sub-division and two recursion paths instead. This reduces the stack depth needed from N to log2 N (or thereabouts).
|Improved recursion used for repeating geometry.|
Recursion is applied to both parts of a central split until there is no more to split.
The other thing we can do is to wrap up the splitting calculations into helper procedures that make it easier to implement these arrays of objects. The general problem here is that we need to be able to have our own geometry within the recursion process which is tricky to support. Instead of having to support embedding of procedures (akin to passing function pointers in code) however, we can provide two procedures, with which we 'book-end' our own geometry generation. These handle the Splitting Logic, and the Combining Logic needed to implement the array process. The general form for this is:
|Layout of a procedure for arraying geometry using the two helper procedures to wrap the recursion and geometry instantiation.|
NOTES: Any external parameters the procedure needs (to customise the generation have to be passed down to the recursion calls too. The Control channel is used to select which of the three outputs are to be combined before returning to the outer procedure, this could be a pair of recursions, or some generated geometry. A further improvement to this process might be to use all three at once when an odd number of elements are present since we can make the splitting even by immediately instantiating geometry for the centre region.s
|Potential further improvement to recursion efficiency.|
These helper procedures I've named 'The Divider' as it divides up space in one direction into equal size pieces for our procedure to build geometry into.
|Basic recursion helper procedure: The Divider (splitting part)|
This is used in conjunction with a 'Merger' which handles aggregation of the elements.
|Basic recursion helper procedure: The Divider (merge part)|
This is a really useful tool to building and distributing content around the world. For example, when a long thin strip of land is encountered in the business district, multiple buildings are placed in a row instead of a single long thin building. Here we see the Divider and Merge stages in use in the Business Block procedure that handles this:
|Divider approach used to create rows of buildings in the business district.|
And here it is in action as the space available changes.
|Array of buildings filling a narrow strip of land using the recursive Divider approach.|
To tackle the fence-post problem, and some of the more sophisticated use-cases, a significantly more powerful version of the divider approach is needed. Here are a couple of examples:
This piece of railing can be sectioned up in a couple of ways, either as the classic fence-post arrangement (circular design 'panels' between flower 'posts'), or by treating the flowers a separators between the circular parts and two end pieces connecting to the walls.
|These railings can be divided up in a couple of ways.|
This building facade can similarly be broken up in to ways, but these are a bit more involved:
|This building facade can be divided up in a couple of ways.|
Here, however we divide it up we have two end-caps (the corners of the building), but the way the wall/windows are divided up can be approached in two ways:
- The window sections are wider and include a bit of wall.
- The wall sections are much cleaner and are present between the end caps and the windows as well as between pairs of window sections.
These requirements can be generalised into the following (optional) sections with what I'm calling 'The Stacker':
- Start cap
- Multiple repetitions of:
- End cap
This can be constructed in a similar fashion to the Divider, but with more user supplied elements in between the helper procedures. This happened to turn out to be the most complicated procedure I'd ever built! I actually tried to tackle this problem a while ago, but decided that it would be impossible without the grouping and notation feature so I set about adding that instead. I'm glad I did now as notes are used extensively to partition the logic and document the processing involved:
|The most complex procedure I've created: 'The Stacker' (splitting part)|
This isn't the most efficient implementation, nor the simplest, I'm sure. But it works, and can be revisited later if it needs speeding up or reducing in size. I could even be re-implemented in code as a build-in operator if needed.
As with the Divider, there is a corresponding re-combination procedure seen here:
|Much simpler companion to The Stacker; the merge part.|
As this was a very complicated procedure, and with many combinations of inputs and options it was imperative to have good test cases. Here we see a large set of instances for most of the various configurations it supports.
|Test cases for The Stacker. Many combinations of the various configurations are tested in one place for easy visual inspection.|
Now we have this powerful tool at our disposal I had a chance to explore what can be done with it.
A straightforward test case is a wall with regular support pillars and larger end columns.
|The Stacker used to implement a wall with regular support and end detail.|
Wrapping the different wall elements in a Stacker and corresponding combiner gives us this procedure:
|Interesting brick wall structure implemented with the Stacker recursion helper procedures.|
Which produces this satisfactory construction.
|Wall design constant parameterisation.|
|Brick Wall procedure expanding to use the space available.|
One of the real test cases I wanted to try out was to build steel-work structures out of girders that can be used as support structures around many industrial components.
|Steel structures of the kind I'd like to use in the industrial district of Future City.|
More specifically, I want to re-create this configuration:
|Example of steel beam configuration I want to produce.|
This is made from steel I-Beam sections and has two stacking aspects to it, horizontally we have:
- (optional) End upright
- Set of cross-members
- separated by uprights
- (optional) End upright
Vertically the cross-members are stacked thus:
- Separated by gaps
This was implemented with a pair of nested procedures, one for horizontal, one for vertical, all contained within a main entry-point procedure.
|Nested horizontal and vertical stacking procedures to create steel-work side wall.|
Here is a selection of constructs built using this set of procedures:
|Random structure variation based around truss, tower, and side procedures.|
|Steel constructs based around a steel-work side section.|
|Truss or gantry built from girders.|
Monday, 12 September 2016
Monday, 5 September 2016
After digging down through the zones and district types, we have some large city regions set out. We now want to break them down into city blocks so that we can start looking at where buildings will go.
The process is similar to the zone sub-division and uses most of the same process and procedures, but this time the design constants are dependent on the district type. For example: residential and leisure areas are probably in smaller blocks than industrial and space-port blocks, with business somewhere in the middle. We can experiment with other differences later on, say, favouring longer thinner leisure areas for parks or squarer business areas suitable for skyscrapers.
|Block design constants, parameterised by district type|
For testing purposes I added a simple cuboid as a placeholder building to each block.
|Simple white-box building added to each block for test purposes|
This is just a proportion of block size for now, with the height chosen randomly. In reality a block may eventually have multiple buildings, but for now I just wanted to get a feel for how the city would look and investigate the detail levels at different distances.
|View across 'white-box city'|
Apparance is built around the premise of bands of detail extending out from the viewpoint, each higher detail one built based on re-synthesising the lower detail procedures. As we start to build more detail into the city we need to begin setting up the integration with the detail management in the engine. Since each re-synthesis is performed using sub-procedures with exactly the same input parameters, something else must provide the ability to change their behaviour as different detail results are required.
|Re-synthesis of procedures for successive depths in the detail hierarchy. How do they know what detail level to generate?|
As the scene is progressively refined to give more detail, the blocks the world is divided up into get smaller. It is this that a procedure can check to decide what level of detail to generate itself at.
For our city blocks we will switch between an extremely low detail (flat) rendition for far in the distance, to our normal block procedure as their size decreases. This will have the effect of gradually populating the area with more buildings as we get closer.
|Switching out the blocks in the distance for a simpler representation.|
The normal blocks intercepted and replaced depending on our detail hierarchy block size.
The Distant Content procedure we are using will make use of a common modelling primitive; a rectangular patch with automatic detail improvement. This also uses this detail switching to break down and subdivide its surface into smaller pieces to add detail and reveal intricacy as you view mode closely. Here we see an example of it increasing in detail.
|Successive refinements of a generic rectangular patch, introducing more detail and some variation.|
Putting this all together and we get a rather satisfying reveal of detail as we move across the city.
|Detail transitions and reveal testing across white-box city|
Setting up the detail management in a scene is quite tricky at the moment. I am still exploring how it can best work and what can be done to improve the user experience. To help understand what the engine and your procedures are doing a lot of diagnostics displays options are available.
|Various diagnostics settings and statistics for a view-port and scene rendering.|
These have been added gradually during the development of the engine and this week I've had to revisit them and add a few features to help fix problems with the detail tracking and blending system. These features are going to be essential in debugging procedures and understanding what the engine is doing with them so it's worth having a look at them now.
There are several colourising modes to visualise various mesh rendering information.
|Colourising of meshes to visualise state and show information spatially|
The scene node hierarchy can be visualised; a progression of hues used to colour each depth level.
|Visualisation of the scene node hierarchy, coloured by depth|
The detail range bands and various transition boundaries can be shown to check where the blends are supposed to be happening.
|Visualisation of the detail tier ranges, coloured by depth|
Most of these displays, as well as models and meshes can be selectively singled out using sliders to help close in on specific issues in the scene. For example, information about, a particular model, in a particular node, in a particular tier of the scene hierarchy can be viewed:
|Focusing in on a specific model in the hierarchy|
Looking at the node diagnostics panel, we see that this model can't be refined any further because the procedures don't have any sub-procedures small enough to fit in the next scene node size down.
|This model in this node can't be subdivided, so no more detail can be generated in this area.|
For more information about the procedures in question and how the analysis for resynthesis worked out we can trigger a re-synthesis and analysis of a model which also allows us to see the evaluation tree (via an external GraphViz step).
|Here we see the refinement capture analysis failing at our temporary content procedure.|
Here it is clear that all the leaf procedures are un-refinable and need more work (which we knew as this is a test procedure of limited ability).
Using the debug camera and some of these diagnostics overlays we can see the detail reveal effect 'from the outside'. Here the details is added and revealed around the view-port after a scene reset. As progressively more detailed versions of the scene are synthesised we can see the extent of each expanding.
|Detail regeneration and reveal after scene reset as seen from external debug camera position.|
These recent posts have been fairly dry and focusing on dividing up spaces rather than the more interesting process of filling them with things. We will start seeing some more exciting things soon, I promise :)